1. Field of the Invention
The present invention relates to ballistic protection structures and more particularly to methods of repairing same.
2. Description of the Prior Art
In my prior patent application Ser. No. 493,323 I have described a ballistic panel utilizing layers of aramid cloth bonded with nylon or a similar plastic. Since that time I have found that laminates of this kind can be successfully combined to effect patches in stress carrying panels perforated by projectiles.
In particular, airplane panels in ground support aircraft often are exposed to opposing ground fire with attendant incidents of damage. Typically, this damage results in stress concentrating fractures which, if not repaired, will propagate and grow with use. Airframes characteristically in the interest of conserving weight, include stressed panels which quite often are bonded to honeycomb backing for taking up transverse loads which, when perforated, is damaged beyond practical repair. The present repair sequences typically entail the replacement of i.e. whole structural section, involving an extensive inventory burden and extensive material support. One should particularly note that the incidence of panel damage is not predictable except through statistical considerations and the practice of replacement of whole structural sections will thus dictate a replacement inventory characterized by the number of unique sections in the vehicle serviced. This, of course, is not acceptable in field applications and solutions to this problem have been sought in the past.
Stressed structures are typically characterized by a panel structure convolved to a geometry dictated by external considerations, like air flow or operating function, the panel being bonded on the interior to stiffening elements often taking the form of thin walled honeycomb. On projectile perforation both the honeycomb backing and the panel are damaged and any repair to the panel necessarily includes some repair or replacement of the loaded backing.
While structures of this kind may be repaired with stiff patches bridging the damaged area, once again, a rather wide complement of variously bent patches is necessary for mating with all the potentially damaged surfaces. Accordingly, repair techniques by which the patch is first formed to fit the shape of the damaged panel and thereafter rendered stiff is both desired and convenient under the foregoing exigencies. It is one such technique that is disclosed herein.